(1) Field of the Invention
The invention relates to a method for manufacturing a permanent-magnet motor rotor.
(2) Field of the Invention
A motor is an electromagnetic device taking magnetic field as media to carry out mutual conversion between mechanical energy and electrical energy. In order to establish an air-gap magnetic field inside of the motor needed by electromechanical energy conversion, two methods are provided. As to one method, a motor winding is energized to generate a magnetic field, such as a conventional DC motor, the motor and so on. This electrically excited motor not only needs a special winding and a corresponding device but also needs to be continuously provided with energy to maintain its current flow. As to the other method, the magnetic field is generated by a permanent magnet. Due to the inherent characteristics of a permanent-magnet material, after it is pre-magnetized (magnetization), it does not need external energy to establish the magnetic field around its surrounding space; that is, it is the so-called permanent magnet motor.
Compared with the conventional excited motor, the permanent magnet motor has the advantages of simple structure, low loss, high power factor, high efficiency, high power density, high starting torque, low temperature, light weight and other obvious characteristics. With the continuous improvement and perfection of the magnetic properties in rare-earth permanent-magnet materials (especially NdFeB) and gradually reduced price, the permanent-magnet motor research and development gradually becomes mature, thus facilitating the permanent magnet motor to be more and more widely used in defense, industrial and agricultural production, daily life and so on.
The permanent-magnet motor is the motor which depends on the permanent magnet on a rotor to generate the magnet field. Its stator structure is basically identical to that of a common synchronous/asynchronous motor. That is, it consists of a stator iron core constituted by stacked silicon steel sheets and a stator coil embedded in an iron-core slot of the stator. It is energized by three-phase alternating current to generate a rotating magnetic field in the stator coil. The permanent-magnet motor rotor mainly consists of a rotor iron core and the permanent magnet, which is the main difference between the permanent-magnet motor and other type of the motor. A rotor magnetic circuit structure is the key technology of the permanent magnet motor. If a magnetic path structure adopted by the rotor is different, the operating performance, the control strategy, the manufacturing process and the use occasion of the motor are also different.
According to different installation locations of the permanent magnet in the permanent magnet motor rotor, the rotor magnetic path of the permanent-magnet motor may generally be divided into three types including a surface type, a built-in type and a claw-pole type. The surface-type rotor magnetic path has the advantages of simple structure and low manufacturing cost. However, as the surface of the rotor may not be mounted with a starting winding, this type permanent-magnet motor does not have asynchronous starting capability. Furthermore, the rotor has worse mechanical strength, and the permanent magnet is easily broken at high rotation speed. The permanent magnet of the built-in type permanent-magnet motor rotor is positioned inside the rotor. According to the relationship between the magnetization direction of the permanent magnet and the rotation direction of the rotor, the magnetic path structure of the built-in type rotor can also be divided into three types including a radial type, a tangential type and a mixed type. Compared with the surface type rotor, the built-in permanent-magnet motor rotor may protect the permanent magnet with the lower mechanical properties. According to performance requirements of the permanent-magnet motor, the size of the permanent magnet may be tremendously increased. Therefore, the structure of the permanent-magnet motor rotor is currently widely used.
At present, the conventional permanent-magnet motor rotor generally adopts a rotor guide strip to fasten the rotor. However, there are still obvious problems of low mechanical strength, poor reliability, severe eddy current loss of the rotor surface, obvious magnetic flux leakage, etc. These hinder the development of the permanent-magnet motor with high power, high speed and large rotary diameter, and further more limit the application of the permanent-magnet motor on high-speed trains as a traction motor.
China patent application No. 201010513307.3 discloses a big-power permanent-magnet motor rotor and a method for mounting the rotor. Adopting a permanent-magnet embedded structure, the rotor consists of at least two rotor units along the axial direction. A magnet-separation groove along the rotor in the axial direction is opened and provided on an iron core between two adjacent permanent magnets of each rotor unit. A spacer made of a non-magnetic material is provided between the adjacent rotor units. An end plate is provided at two ends of the rotor unit. At least two rotor units are fixed through axially positioned tightening bolt.
The permanent-magnet rotor has the following disadvantages: 1. The centrifugal force stressed by a rotor pole shoe is born jointly by an end plate, the spacer and a positioning tightening bolt. That is, the positioning tightening bolt fixing the rotor unit needs to bear bending moment. When the rotor rotates at high speed, the centrifugal force is so large that the positioning tightening bolt is easily to be bended by the centrifugal force. That is, the rotor does not apply to the motor with high speed rotation. 2. Although the magnet-separation groove is opened and provided at the iron core, the iron core, between the adjacent permanent magnet, still has a connection part. The magnetic field of the permanent magnet of adjacent poles, through the direct communication of the iron core between the permanent magnets, causes magnetic flux leakage. That is, the structure cannot avoid magnetic flux leakage and has serious magnetic flux leakage. 3. The spacer is provided between two adjacent rotor units. The thickness of the spacer occupies the effective length of the rotor in the axial direction. When the number of the rotor units of the adopted rotor is increased and the thickness of the rotor spacer is increased, the effective length is dramatically reduced, thus affecting the electromagnetic properties of the rotor.